Jeremy Corbyn at a remain event in the run-up to the EU referendum. His deputy hinted that a policy shift on Brexit could still be on the table.
Photograph: UPI/Barcroft Images

The number of Labour leave voters in each constituency could be lower than previously thought, suggesting MPs in pro-Brexit seats who fear being punished at the ballot box unless they adopt a hardline stance could be worrying unnecessarily, a campaign group has said.

In a study of all 650 UK parliamentary seats, the pro-remain group Best for Britain found numerous examples of Labour-held constituencies where remain supporters outnumber the MP’s majority.

The group has briefed many MPs on its findings in the hope of emboldening Labour politicians who had been reluctant to push the party leadership to support staying in the European Economic Area because of constituents’ views.

Quick guide

What are Brexit options now? Four scenarios

Staying in the single market and customs union

The UK could sign up to all the EU’s rules and regulations, staying in the single market – which provides free movement of goods, services and people – and the customs union, in which EU members agree tariffs on external states. Freedom of movement would continue and the UK would keep paying into the Brussels pot. We would continue to have unfettered access to EU trade, but the pledge to “take back control” of laws, borders and money would not have been fulfilled. This is an unlikely outcome and one that may be possible only by reversing the Brexit decision, after a second referendum or election.

The Norway model

Britain could follow Norway, which is in the single market, is subject to freedom of movement rules and pays a fee to Brussels – but is outside the customs union. That combination would tie Britain to EU regulations but allow it to sign trade deals of its own. A “Norway-minus” deal is more likely. That would see the UK leave the single market and customs union and end free movement of people. But Britain would align its rules and regulations with Brussels, hoping this would allow a greater degree of market access. The UK would still be subject to EU rules.

The Canada deal

A comprehensive trade deal like the one handed to Canada would help British traders, as it would lower or eliminate tariffs. But there would be little on offer for the UK services industry. It is a bad outcome for financial services. Such a deal would leave Britain free to diverge from EU rules and regulations but that in turn would lead to border checks and the rise of other “non-tariff barriers” to trade. It would leave Britain free to forge new trade deals with other nations. Many in Brussels see this as a likely outcome, based on Theresa May’s direction so far.

No deal

Britain leaves with no trade deal, meaning that all trade is governed by World Trade Organization rules. Tariffs would be high, queues at the border long and the Irish border issue severe. In the short term, British aircraft might be unable to fly to some European destinations. The UK would quickly need to establish bilateral agreements to deal with the consequences, but the country would be free to take whatever future direction it wishes. It may need to deregulate to attract international business – a very different future and a lot of disruption.

Seven in 10 Labour-held constituencies voted to leave the EU and a recent meeting of the parliamentary Labour party was dominated by a bitter row over the single market, with MPs in pro-Brexit seats warning that supporting it would damage their electoral chances.

However, the research suggested there were “only a handful” of seats where more Labour voters backed leave than remain, and that many of these would support the party at a general election irrespective of its position on Brexit.

The study, which used YouGov data, showed that key members of Corbyn’s inner circle were among those MPs who could benefit from an “electoral dividend” if the party softened its position on Brexit. They included the shadow cabinet ministers Jon Trickett and Ian Lavery.

Corbyn under pressure to give members vote on Labour Brexit policy

Read more

Trickett’s Hemsworth seat in West Yorkshire voted by 68.1% to leave the EU at the 2016 referendum. However, the YouGov data shows that of those who voted in the 2017 election, 11,037 were Labour remainers, greater than the shadow cabinet minister’s 10,174 majority. More Labour voters in the constituency backed remain than leave.

Lavery’s Wansbeck constituency in Northumberland backed Brexit with a 56.2% vote, yet the Labour remain tally was 12,392, greater than the Labour party chairman’s 10,435 majority. In 2017, 51% of Labour voters in the election had backed remain at the referendum, while 32% supported leave.

An insider at Best for Britain said: “These are both seats where the MP has the ear of Jeremy Corbyn. In each, the MP’s position is better than previously thought. If you’re saying that about Wansbeck and Hemsworth, then you can also say it about a couple of hundred other Labour-held seats with the same dynamic.”

These could include Don Valley, where the Labour MP Caroline Flint campaigned for remain but has subsequently warned the party not to try to “wriggle out” of the referendum result. Her constituency voted leave by 68.6%, but the Labour remain vote in 2017 was, at 10,371, substantially larger than her 5,169 majority.

Best for Britain, which was set up by the pro-EU campaigner Gina Miller, also held focus groups that suggested Labour leave voters would vote for a Labour government even if its position on Brexit – which is currently to stay in a customs union – did change.

The data, which cost tens of thousands of pounds to produce, also suggests many Conservative MPs have more Tory remain voters than previously thought, potentially bringing some of these seats into play for Labour.

The Tory Brexiter Stuart Andrew, for example, has a majority of just 331 in Pudsey in West Yorkshire. However, 6,903 Tory voters in 2017 were backers of remain. The former Tory leader Iain Duncan Smith also has more Tory remainers in his Chingford and Woodford Green seat than his 2,438 majority.

Best for Britain also believes the research might “stiffen the resolve” of remain-supporting Tory MPs to consider their options when the House of Commons votes on Brexit in the next two weeks.

The research highlights the chances of a Labour “decapitation strategy” against Boris Johnson, whose majority in Uxbridge and South Ruislip halved at the last election to 5,034. The Tory remain vote there stood at 5,444 in 2017.

It showed that Theresa May has the second highest Tory remain vote in the country in Maidenhead, with 14,452 of her backers also voting to stay in the EU.

Eloise Todd, the chief executive of Best for Britain, said: “This is the first batch of a massive research project that we have undertaken. What this shows is that there is an electoral dividend for Labour in many seats if they move position and oppose Brexit. Not only is it right for the country for Labour to do that, it’s also good for Labour.”